Optimized fuel management system for direct injection ethanol enhancement of gasoline engines

ABSTRACT

Fuel management system for enhanced operation of a spark ignition gasoline engine. Injectors inject an anti-knock agent such as ethanol directly into a cylinder. It is preferred that the direct injection occur after the inlet valve is closed. It is also preferred that stoichiometric operation with a three way catalyst be used to minimize emissions. In addition, it is also preferred that the anti-knock agents have a heat of vaporization per unit of combustion energy that is at least three times that of gasoline.

This application is a confirmation of U.S. patent application Ser. No.13/546,220 filed on Jul. 11, 2012, which is a continuation of U.S.patent application Ser. No. 12/701,034 filed on Feb. 5, 2010 which is acontinuation of U.S. patent application Ser. No. 11/758,157 filed Jun.5, 2007, which is a continuation of U.S. patent application Ser. No.11/100,026, filed Apr. 6, 2005, now U.S. Pat. No. 7,225,787, which is acontinuation-in-part of U.S. patent application Ser. No. 10/991,774filed Nov. 18, 2004, now U.S. Pat. No. 7,314,033, the contents of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to an optimized fuel system for use with sparkignition gasoline engines in which an anti-knock agent which is a fuelis directly injected into a cylinder of the engine.

There are a number of important additional approaches for optimizingdirect injection ethanol enhanced knock suppression so as to maximizethe increase in engine efficiency and to minimize emissions of airpollutants beyond the technology disclosed in parent application Ser.No. 10/991,774 set out above. There are also additional approaches toprotect the engine and exhaust system during high load operation byethanol rich operation; and to minimise cost, ethanol fuel use andethanol fuel storage requirements. This disclosure describes theseapproaches.

These approaches are based in part on more refined calculations of theeffects of variable ethanol octane enhancement using a new computermodel that we have developed. The model determines the effect of directinjection of ethanol on the occurrence of knock for different times ofinjection and mixtures with port fuel injected gasoline. It determinesthe beneficial effect of evaporative cooling of the direct ethanolinjection upon knock suppression.

SUMMARY OF THE INVENTION

In one aspect, the invention is a fuel management system for operationof a spark ignition gasoline engine including a gasoline engine and asource of an anti-knock agent which is a fuel. The use of the anti-knockagent provides gasoline savings both by facilitating increased engineefficiency over a drive cycle and by substitution for gasoline as afuel. An injector is provided for direct injection of the anti-knockagent into a cylinder of the engine and a fuel management control systemcontrols injection of the anti-knock agent into the cylinder to controlknock. The injection at the antiknock agent can be initiated by a signalfrom a knock sensor. It can also be initiated when the engine torque isabove a selected value or fraction of the maximum torque where the valueor fraction of the maximum torque is a function of the engine speed. Ina preferred embodiment, the injector injects the anti-knock agent afterinlet valve/valves are closed. It is preferred that the anti-knock agenthave a heat of vaporization that is at least twice that of gasoline or aheat of vaporization per unit of combustion energy that is at leastthree times that of gasoline. A preferred anti-knock agent is ethanol.In a preferred embodiment of this aspect of the invention, part of thefuel is port injected and the port injected fuel is gasoline. Thedirectly injected ethanol can be mixed with gasoline or with methanol.It is also preferred that the engine be capable of operating at amanifold pressure at least twice that pressure at which knock wouldoccur if the engine were to be operated with naturally aspiratedgasoline. A suitable maximum ethanol fraction during a drive cycle whenknock suppression is desired is between 30% and 100% by energy. It isalso preferred that the compression ratio be at least 10. With thehigher manifold pressure, the engine can be downsized by a factor of twoand the efficiency under driving conditions increased by 30%.

It is preferred that the engine is operated at a substantiallystoichiometric air/fuel ratio during part of all of the time that theanti-knock agent such as ethanol is injected. In this case, a three-waycatalyst can be used to reduce the exhaust emissions from the engine.The fuel management system may operate in open or closed loop modes.

In some embodiments, non-uniform ethanol injection is employed. Ethanolinjection may be delayed relative to bottom dead center when non-uniformethanol distribution is desired.

Many other embodiments of the invention are set forth in detail in theremainder of this application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of ethanol fraction (by energy) required to avoidknock as a function of inlet manifold pressure. The ethanol fraction isshown for various values of β, the ratio of the change in temperature inthe air cylinder charge due to turbocharging (and aftercooling if used)to the adiabatic temperature increase of the air due to theturbocharger.

FIG. 2 a is a graph of cylinder pressure as a function of crank anglefor a three bar manifold pressure.

FIG. 2 b is a graph of charge temperature as a function of crank anglefor a three bar manifold pressure.

FIG. 3 is a schematic diagram of an embodiment of the fuel managementsystem disclosed herein for maintaining stoichiometric conditions withmetering/control of ethanol, gasoline, and air flows into an engine.

FIGS. 4 a and 4 b are schematic illustrations relating to the separationof ethanol from ethanol/gasoline blends.

FIG. 5 is a cross-sectional view of a flexible fuel tank for a vehicleusing ethanol boosting of a gasoline engine.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Ethanol has a heat of vaporization that is more than twice that ofgasoline, a heat of combustion per kg which is about 60% of that ofgasoline, and a heat of vaporization per unit of combustion energy thatis close to four times that of gasoline. Thus the evaporative cooling ofthe cylinder air/fuel charge can be very large with appropriate directinjection of this antiknock agent. The computer model referenced belowshows that evaporative cooling can have a very beneficial effect onknock suppression. It indicates that the beneficial effect can bemaximized by injection of the ethanol after the inlet valve that admitsthe air and gasoline into the cylinder is closed. This late injection ofthe ethanol enables significantly higher pressure operation withoutknock and thus higher efficiency engine operation than would be the casewith early injection. It is thus preferred to the conventional approachof early injection which is used because it provides good mixing. Themodel also provides information that can he used for open loop (i.e., acontrol system that uses predetermined information rather than feedback)fuel management control algorithms.

The increase in gasoline engine efficiency that can be obtained fromdirect injection of ethanol is maximized by having the capability forhighest possible knock suppression enhancement. This capability allowsthe highest possible amount of torque when needed and therebyfacilitates the largest engine downsizing for a given compression ratio.

Maximum knock suppression is obtained with 100% or close to 100% use ofdirect injection of ethanol. A small amount of port injection ofgasoline may be useful in order to obtain combustion stability byproviding a more homogeneous mixture. Port fuel injection of gasolinealso removes the need for a second direct fuel system or a morecomplicated system which uses one set of injectors for both fuels. Thiscan be useful in minimizing costs.

The maximum fraction of ethanol used during a drive cycle will dependupon the engine system design and the desired level of maximum torque atdifferent engine speeds. A representative range for the maximum ethanolfraction by energy is between 20% and 100%.

In order to obtain the highest possible octane enhancement while stillmaintaining combustion stability, it may be useful for 100% of the fuelto come from ethanol with a fraction being port injected, as analternative to a small fraction of the port-fueled gasoline.

The initial determination of the knock suppression by direct injectionof ethanol into a gasoline engine has been refined by the development ofa computer model for the onset of knock under various conditions. Thecomputer modeling provides more accurate information for use in fuelmanagement control. It also shows the potential for larger octaneenhancements than our earlier projections. Larger octane enhancementscan increase the efficiency gain through greater downsizing and highercompression ratio operation. They can also reduce the amount of ethanoluse for a given efficiency increase.

The computer model combines physical models of the ethanol vaporizationeffects and the effects of piston motion of the ethanol/gasoline/airmixtures with a state of the art calculational code for combustionkinetics. The calculational code for combustion kinetics was the enginemodule in the CHEMKIN 4.0 code [R. J. Kee, F. M. Rupley, J. A. Miller,M. E. Coltrin, J. F. Grear, E. Meeks, H. K. Moffat, A. E. Lutz, G.Dixon-Lewis, M. D. Smooke, J. Warnatz, G. H. Evans, R. S. Larson, R. E.Mitchell, L. R. Petzold, W. C. Reynolds, M. Caracotsios, W. E. Stewart,P. Glarborg, C. Wang, O. Adigun, W. G. Houf, C. P. Chou, S. F. Miller,P. Ho, and D. J. Young, CHEMKIN Release. 4.0, Reaction Design, Inc., SanDiego, Calif. (2004)]. The CHEMKIN code is a software tool for solvingcomplex chemical kinetics problems. This new model uses chemical ratesinformation based upon the Primary Reference gasoline Fuel (PRF)mechanism from Curran et al. [Curran, H. J., Gaffuri, P., Pitz, W. J.,and Westbrook, C. K. “A Comprehensive Modeling Study of iso-OctaneOxidation,” Combustion and Flame 129:253-280 (2002) to represent onsetof autoignition.

The compression on the fuel/air mixture end-gas was modeled using theartifact of an engine compression ratio of 21 to represent theconditions of the end gas in an engine with an actual compression ratioof 10. The end gas is defined as the un-combusted air/fuel mixtureremaining after 75% (by mass) of the fuel has combusted. It is the endgas that is most prone to autoignition (knock). The larger compressionratio includes the effect of the increase in pressure in the cylinderdue to the energy released in the combustion of 75% of the fuel that isnot in the end gas region. The effect of direct ethanol vaporization ontemperature was modeled by consideration of the effects of the latentheat of vaporization on temperature depending upon the time of theinjection.

The effect of temperature increase due to turbocharging was alsoincluded. The increase in temperature with turbocharging was calculatedusing an adiabatic compression model of air. It is assumed that thermaltransfer in the piping or in an intercooler results in a smallertemperature increase. The effect is modeled by assuming that theincrease in temperature of the air charge into the cylinder ΔT_(charge)is ΔT_(charge)=βΔT_(turbo) where ΔT_(turbo) is the temperature increaseafter the compressor due to boosting and beta is a constant. Values of βof 0.3, 0.4 and 0.6 have been used in the modeling. It is assumed thatthe temperature of the charge would be 380 K for a naturally aspiratedengine with port fuel injection gasoline.

FIG. 1 shows the predictions of the above-referenced computer model forthe minimum ethanol fraction required to prevent knock as a function ofthe pressure in the inlet manifold, for various values of β. In FIG. 1it is assumed that the direct injection of the ethanol is late (i.e.after the inlet valve that admits air and gasoline to the cylinder isclosed) and a 87 octane PRF (Primary Reference Fuel) to representregular gasoline. The corresponding calculations for the manifoldtemperature are shown in Table 1 for the case of a pressure in the inletmanifold of up to 3 bar for an engine with a conventional compressionratio of 10. The temperature of the charge varies with the amount ofethanol directly injected and is self-consistently calculated in Table 1and FIG. 1. The engine speed used in these calculations is 1000 rpm.

TABLE 1 Computer model calculations of temperature and ethanol fractionrequired for knock prevention for an inlet manifold pressure of 3 barfor an engine with a compression ratio of 10, for various values of β(ratio of change of the cylinder air charge temperature due toturbocharging to the adiabatic temperature increase due to turbochargingΔT_(charge) = βΔT_(turbo)). The engine speed is 1000 rpm. β 0.3 0.4 0.6T_charge init K 380 380 380 Delta T turbo K 180 180 180 Delta T afterintercooler K 54 72 108 Delta T due to DI ethanol and gasoline K −103−111 −132 T_init equivalent charge K 331 341 356 Gasoline octane 87 8787 Ethanol fraction (by energy) needed 74% 82% 97% to prevent knock

Direct fuel injection is normally performed early, before the inletvalve is closed in order to obtain good mixing of the fuel and air.However, our computer calculations indicate a substantial benefit frominjection after the inlet valve is closed.

The amount of air is constant in the case of injection after the inletvalve has closed. Therefore the temperature change is calculated usingthe heat capacity of air at constant volume (c_(v)). The case of earlyinjection where the valve that admits air and fuel to the cylinder isstill open is modeled with a constant-pressure heat capacity (c_(p)).The constant volume case results in a larger evaporation induceddecrease in charge temperature than in the case for constant pressure,by approximately 30%. The better evaporative cooling can allow operationat higher manifold pressure (corresponding to a greater octaneenhancement) without knock that would be the case of early injection bya difference of more than 1 bar. The increase in the evaporative coolingeffect at constant volume relative to that at constant pressure issubstantially higher for the case of direct injection of fuels such asethanol and methanol than is the case for direct injection of gasoline.

Typical results from the calculations are shown in FIG. 2. The figureshows the pressure (a) and the temperature (b) of the cylinder charge asa function of crank angle, for a manifold pressure of 3 bar and a valueof β=0.4. Two values of the ethanol fraction are chosen, one thatresults in autoignition, and produces engine knock (0.82 ethanolfraction by fuel energy), and the other one without autoignition, i.e.,no knock (0.83 ethanol fraction). Autoignition is a thresholdphenomenon, and in this case occurs between ethanol fractions of 0.82and 0.83. For an ethanol energy fraction of 0.83, the pressure andtemperature rise at 360° (top dead center) is due largely to thecompression of the air fuel mixture by the piston. When the ethanolenergy fraction is reduced to 0.82, the temperature and pressure spikesas a result of autoignition. Although the autoignition in FIG. 2 occurssubstantially after 360 degrees, the autoignition timing is verysensitive to the autoignition temperature (5 crank angle degrees changein autoignition timing for a change in the initial temperature of 1 K,or a change in the ethanol energy fraction of 1%).

The effect of evaporative cooling from the antiknock agent (in thiscase, ethanol) is shown in Table 2, where three cases are compared. Thefirst one is with port fuel injection of ethanol. In this case thevaporization of the ethanol on the walls of the manifold has anegligible impact on the temperature of the charge to the cylinderbecause the walls of the manifold are cooled rather than the air charge.The second case assumes direct injection, but with the inlet valve open,with evaporation at constant pressure, where the cooling of the chargeadmits additional air to the cylinder. The third case assumes, as in theprevious discussions, late injection after the inlet valve has closed.It is assumed stoichiometric operation, that the baseline temperature is380 K, and that there is cooling in the manifold after the turbochargerwith β=0.4.

TABLE 2 Knock free operation of ethanol port fuel injection (assuming nocharge cooling) and of direct injection before and after the inlet valveis closed. Compression ratio of 10, baseline charge temperature of 380K, intercooler/cooling post turbo with β = 0.4, stoichiometricoperation, gasoline with 87 RON. Engine speed is 1000 rpm. Evaporativecooling No Evaporative Before After Cooling Valve Closing Valve ClosingEthanol fraction 0.95 0.95 0.95 (by energy) Max manifold pressure 1.052.4 4.0 (bar) Cylinder pressure after 1.05 2.4 3.0 cooling (bar)Cylinder charge 383 360 355 temperature after cooling (K)

The results indicate the strong effect of the cooling. The maximummanifold pressure that prevents knock (without spark retard), with 0.95ethanol fraction by energy in the case of port fuel injection is 1.05bar. With direct injection of the ethanol, the maximum knock-freemanifold and cylinder pressures are 2.4 bar, with a temperature decreaseof the charge of ˜75K. The final case, with injection after inlet valvedosing, allows a manifold pressure of 4 bar, a cylinder pressure (aftercooling) of 3 bar, and a charge temperature decrease of ˜120K. It shouldbe noted that the torque of the late injection case after the valve hasclosed is actually higher than that of the early injection case, eventhough the early injection case allows for additional air (at constantpressure). For comparison, the model is also used to calculate themanifold pressure at which knock would occur for port fuel injection of87 octane gasoline alone. This pressure is ˜0.8 bar assuming sparktiming at MBT (Maximum Brake Torque). Conventional gasoline enginesoperate at 1 bar by retarding the timing at high torque regions whereknock would otherwise occur. Thus the model indicates that evaporativecooling effect of direct injection of ethanol after the inlet valve hasclosed can be significantly greater than that of the higher octanenumber rating of ethanol relative to gasoline.

A manifold pressure of 4 bar is very aggressive. Table 2 is indicativeof the dramatically improved performance of the system with directinjection after the inlet valve has closed. The improved performance inthis case can be traded for increased compression ratio or reduced useof the anti-knock agent.

It should be noted that, as mentioned above, the calculations ofautoignition (knock) are conservative, as autoignition for the caseshown in FIG. 2 occurs relatively late in the cycle, and it is possiblethat the fuel has been combusted before it autoignites. Also it shouldbe noted that the calculations in FIG. 2 break down after autoignition,as the pressure trace would be different from that assumed. Figuressimilar to FIG. 2 are used to determine conditions where autoignitionwould not occur, and those conditions are then used to provide theinformation for FIG. 1. The initial temperatures of the cases shown inFIG. 2 are 341 K for 0.82 ethanol fraction, and 340 K for 0.83 ethanolfraction, a difference of 1K (the difference due to the cooling effectof the ethanol).

Because of the large heat of vaporization, there could be enough chargecooling with early injection so that the rate of vaporization of ethanolis substantially decreased. By instead injecting into the hot gases,which is the case with injection after the inlet valve has closed, thetemperature at the end of full vaporization of the ethanol issubstantially increased with respect to early injection, increasing theevaporation rate and minimizing wall wetting.

The optimum timing of the injection for best mixing and a nearhomogeneous charge is soon after the inlet valve closes, provided thatthe charge is sufficiently warm for antiknock agent vaporization. If, onthe other hand, a non-uniform mixture is desired in order to minimizeethanol requirements and improve ignition stability, then the injectionshould occur later than in the case where the best achievable mixing isthe goal.

Late injection of the ethanol after the inlet valve has closed can beoptimized through the use of diesel-like injection schemes, such asinjectors with multiple sprays. It is important to inject the fuelrelatively quickly, and at velocities which minimize any cylinder wallwetting, which as described below could result in the removal of thelubrication oils from the cylinder liner. Multiple sprays from a nozzlethat has multiple holes results in a distributed pattern of sprays, withrelatively low injection velocities. This is particularly important forethanol, because of the higher volume throughputs (as compared withgasoline) of ethanol for equal energy content.

Injection after the valve has closed may require that a modest fractionof the fuel (e.g. 25%) be port injected in order to achieve the desiredcombustion stability. A tumble-like or swirl motion can be introduced toachieve the desired combustion stability. The port injected fuel can beeither gasoline or ethanol.

Use of the computer model for operation with gasoline alone givesresults that are consistent with the observed occurrence of knock ingasoline engine vehicles, thereby buttressing the credibility of theprojections for ethanol. The computer model indicates that forknock-free gasoline operation alone with a compression ratio of 10,knock imposes a severe constraint upon the allowed manifold pressure fora naturally aspirated gasoline engine and very limited (i.e., less than1.2 bar) manifold pressure can be achieved even with direct injection ofgasoline unless spark retard and/or rich operation is used. Thesechanges, however, can reduce efficiency and increase emissions.

FIG. 1 shows that knock can be prevented at manifold pressures greaterthan 2 bar with direct injection of an ethanol fraction of between 40and 80% in an engine with a compression ratio of 10. The manifoldpressure can be at least 2.5 bar without engine knock. A pressure of 3bar would allow the engine to be downsized to ˜⅓ of the naturallyaspirated gasoline engine, while still producing the same maximum torqueand power. The large boosting indicated by the calculations above mayrequire a multiple-stage turbocharger. In addition to a multiple stageturbocharger, the turbocharger may be of the twin-scroll turbo type tooptimize the turbocharging and decrease the pressure fluctuations in theinlet manifold generated by a small number of cylinders.

With an increase in allowed manifold pressure in an engine by more thana factor of 2, the engine could be downsized by a factor of 2 (that is,the cylinder volume is decreased by a factor of 2 or more) and thecompression ratio could be held constant or raised. For example, theperformance of an eight cylinder engine is achieved by a four cylinderengine.

The occurrence of knock at a given value of torque depends upon enginespeed. In addition to providing substantially more maximum torque andpower, direct injection of ethanol can be used to provide a significantimprovement in torque at low engine speeds (less than 1.500 rpm) bydecreasing or eliminating the spark retard. Spark retard is generallyused with gasoline engines to prevent knock at low engine speeds whereautoignition occurs at lower values of torque than is the case at highengine speeds.

FIG. 1 can also be used to determine the ethanol fraction required toprevent knock at different levels of torque and horsepower, which scalewith manifold pressure in a given size engine. This information can beused in an open loop control system.

The efficiency of a gasoline engine under driving conditions usingdirect ethanol injection enhancement can be at least 20% and preferablyat least 30% greater than that of a naturally aspirated gasoline enginewith a compression ratio of 10. This increase results from thesubstantial engine boosting and downsizing to give the same power, andalso the high compression ratio operation (compression ratio of 11 orgreater) that is enabled by a large octane enhancement. With moreaggressive downsizing of more than 50% (where the same engineperformance is obtained with less than one-half the displacement), theincrease in efficiency could exceed 30%.

Greater downsizing and higher efficiency may also be obtained bydecreasing the octane requirement of the engine by using variable valvetiming (VVT). Thus, at conditions of high torque, variable valve timingcan be used to decrease the compression ratio by appropriately changingthe opening/closing of the inlet and exhaust valves. The loss inefficiency at high torque has a small impact on the overall fuel economybecause the engine seldom operates in these conditions.

VVT can also be used to better scavenge the exhaust gases [B. Lecointeand G. Monnier, “Downsizing a Gasoline Engine Using Turbocharging withDirect Injection” SAE paper 2003-01-0542]. Decreasing the exhaust gasdecreases the air/fuel temperature. Keeping both the inlet and exhaustvalves open, while the pressure in the inlet manifold is higher than inthe exhaust, can be used to remove the exhaust gases from the combustionchamber. This effect, coupled with slightly rich operation in-cylinder,can result in increased knock avoidance while the exhaust is stillstoichiometric. Cooled EGR and spark timing adjustment can also be usedto increase knock avoidance.

Any delay in delivering high engine torque at low engine speeds candecrease drivability of the vehicle. Under these conditions, because ofthe substantial engine downsizing, the vehicle would have insufficientacceleration at low engine speeds until the turbo produces highpressures. This delay can be removed through the use of direct injectionof ethanol by reduction of the spark retard or ethanol/gasoline withrich operation and also with the use of variable valve timing.

Another approach would be to use an electrically assisted turbo charger.Units that can generate the required boosting for short periods of timeare available. The devices offer very fast response time, although theyhave substantial power requirements.

A multiple scroll turbocharger can be used to decrease the pressurefluctuations in the manifold that could result from the decreased numberof cylinders in a downsized engine.

The temperature of the air downstream from the turbocharger is increasedby the compression process. Use of an intercooler can prevent thistemperature increase from increasing the engine's octane requirement. Inaddition, in order to maximize the power available from the engine for agiven turbocharging, cooling of the air charge results in increased massof air into the cylinder, and thus higher power.

In order to minimize emissions, the engine should be operatedsubstantially all of the time, or most of the time, with astoichiometric air/fuel ratio in order that a 3-way exhaust catalysttreatment can he used. FIG. 3 shows a 3-way exhaust treatment catalyst10 and air, gasoline and ethanol control needed to maintain thesubstantially stoichiometric ratio of fuel to air that is needed for itseffective operation. The system uses an oxygen sensor 12 as an input toan electronic control unit (ECU) 14. The ECU 14 controls the amount ofair into a turbocharger 16, the amount of gasoline and the amount ofethanol so as to insure stoichiometric operation. During transients,open-loop algorithms from a stored engine map (not shown) are used todetermine air, gasoline and ethanol flows for keeping substantiallystoichiometric combustion in a cylinder of the engine 18.

Thus when variable ethanol octane enhancement is employed, the fuelmanagement system needs to adjust the amounts of air, gasoline andethanol such that the fuel/air ratio is substantially equal to 1. Theadditional control is needed because, if the air/gasoline ratiodetermined by the fuel management were not be corrected during theinjection of ethanol, the mixture would no longer be stoichiometric. Incontrast to the lean boost approach of Stokes et al. [J. Stokes, T. H.Lake and R. J. Osborne, “A Gasoline Engine Concept for Improved FuelEconomy—The Lean Boost System,” SAE paper 2000-01-2902] stoichiometricoperation with a 3-way catalyst results in very low tailpipe emissions.

There are certain regions in the engine operating map where the ECU 14may operate open loop, that is, the control is determined by comparisonto an engine map lookup table rather than by feedback from a sensedparameter which in this case is engine knock (closed loop). As mentionedpreviously, open loop operation during transients may be advantageous.

Another situation where open loop control can be advantageous would beunder high load, where fuel rich conditions (where the fuel/air ratio isgreater than stoichiometric) may be required to decrease the temperatureof the combustion and thus protect the engine and the exhaust system(especially during prolonged operation). The conventional approach ingasoline engine vehicles is to use increased fuel/air ratio, that is,operating at rich conditions. The presence of ethanol on-board allowsfor two alternatives. The first is the use of ethanol fuel fractionsbeyond what is required to control knock, thus reducing the combustiontemperature by a greater amount than could be obtained by gasoline alonedue to the higher cooling effect of evaporation in direct ethanolinjection, even while at stoichiometric conditions. The second one is,as in conventional applications, the use of increased fueling in richoperation (which could result in relative air/fuel mass ratios as low as0.75 where a stoichiometric mixture has a relative air/fuel ratio of 1).The control system can choose between two fuels, ethanol and gasoline.Increased use of ethanol may be better than use of gasoline, withemissions that are less damaging to the environment than gasoline anddecreased amount of rich operation to achieve the temperature controlneeded. Open loop operation with both gasoline and ethanol may requiresubstantial modification of the engine's “lookup table.”

Thus, a method of operating an engine is, under conditions of partialload, to operate closed loop with the use of only gasoline. As theengine load increases, the engine control system may change to open loopoperation, using a lookup table.

The closed loop control of the engine can be such that a knock sensor(not shown) determines the fraction required of ethanol, while theoxygen sensor 12 determines the total amount of fuel. A variation ofthis scheme is to operate the knock control open loop, using a lookuptable to determine the ethanol to gasoline ratio, but a dosed loop todetermine the total amount of fuel.

In order to minimize evaporative emission of the ethanol (which has arelatively low boiling point), solvents can be added to the ethanol tominimize the effect. An alternative means is to place an absorptivecanister between the ethanol tank and the atmosphere that captures theethanol and releases it when the engine is operational.

Because of the large cooling effect from ethanol, it has been known forsome time that startup of a cold engine is difficult (for example,during the first 30 seconds). With the multiple fuels, it is possible tostart up the engine without ethanol addition. Gasoline vaporizes easierthan ethanol, and conventional operation with port-fuel or directinjected gasoline would result in easier engine start up. A greaterfraction of gasoline than would be ordinarily used can be used tofacilitate start-up operation at times during the first 30 seconds ofengine operation.

Increased efficiency due to engine downsizing made possible through theuse of 100% or close to 100% ethanol at the highest values of torque hasthe undesirable effect of requiring higher ethanol fractions. Hence theuse of non-uniform ethanol distribution to minimize the use of ethanolat these values of torque becomes more attractive when achievement ofthe maximum efficiency gain is desired.

Below a certain value of torque or boost pressure it can be advantageousto use a non-uniform ethanol distribution in order to reduce the amountof ethanol that is used. Above certain torque or turbocharger orsupercharger boost pressures, non-uniform charge would not be used sincethe engine is operating mostly on ethanol and ethanol non-uniformitycannot be used for minimizing ethanol consumption. This is especiallyimportant if the desired fraction is higher than 50%.

The capability to minimize the use of ethanol by non-uniform ethanoldistribution in the cylinder can be realized by certain ethanolinjection geometries. Ethanol can be injected in the periphery of aswirling charge. In order to minimize wall wetting by the ethanol, itwould be convenient to achieve the injection in a manner such that theethanol injection matches the swirling motion of the charge. Theinjection direction is thus positioned at an angle with respect to themain axis of the cylinder, injecting the ethanol with an angulardirection component. Charge stratification in the case of swirl can bemaintained by temperature stratification, with the cooler (and denser)regions in the periphery, which correspond to the end-gas zone.

An alternative or additional method to provide ethanol non-uniformdistribution in the cylinder is to inject the ethanol relatively latewith respect to bottom dead center. Thus the time for transport anddiffusion of the ethanol is minimized. However, sufficient time shouldbe allowed for full vaporization of the ethanol. As the temperatures arehigher after Bottom-Dead-Center (BDC), the vaporization time is reduced,and it is less likely that the ethanol would wet the cylinder walls.Improved vaporization of the ethanol can also be achieved by usinginjectors that produce small droplets. The injector could be a singlespray pattern injector with a relatively narrow directed jet. This typeof jet would optimize the deposition of the ethanol in the desiredregion.

Creating a non-uniform ethanol distribution in the cylinder (in theouter regions of the cylinder) has two advantages. The first one is theincreased cooling effect of the region that has the propensity toautoignite (knock), the end gas region. The second is that the centralregion is not cooled, improving ignition and initial flame propagation.It is preferable to keep the central region hot, as having a fast flamespeed early in the flame propagation has antiknock advantages, byreducing the burn time and the time for precombustion chemistry of theend gas. Minimizing the burn time decreases the propensity to knock, asthere is no knock if the end gas is burned before it can autoignite.Thus it is possible to have good ignition properties of the air/fuelmixture, even under conditions where the gasoline is evenly spreadthroughout the cylinder.

Stratified operation can result in locally increased charge cooling.This is because the injected ethanol cools only a small fraction of thecharge, and thus, for a given amount of ethanol, the local decrease intemperature is larger with stratified operation than the averagedecrease of temperature with uniform ethanol distribution. Lateinjection can aid in the formation of a non-uniform air/ethanol mixtureas mixing time is limited. Since a fraction of the gasoline is port-fuelinjected, it can be assumed that this fuel is homogeneously distributedin the cylinder, but ethanol is preferentially in the cooler edges (theend-gas). Thus, although overall the air/fuel charge is stoichiometric,locally near the spark. It is lean while in the region of the end gas itis rich. Both of these conditions are advantageous, since the ignitionoccurs in a region with higher temperature (although slightly lean),while the outside is rich and cool, both of which are knock-suppressors.

In the case of swirl or tumble stratified air fuel charges with hotair/gasoline in the center and colder air/ethanol orair/ethanol/gasoline mixtures in the end gas, it is advantageous toplace the spark in the region of the hot air/gasoline mixture(substantially near the center of the combustion chamber).

Ethanol consumption can be minimized if the gasoline is also directlyinjected. In this case, the heat of vaporization of gasoline is alsouseful in decreasing the temperature of the charge in the cylinder. Thegasoline can be injected using a separate set of injectors. This wouldprovide the most flexibility. However, it may be difficult to fit twosets of injectors per cylinder in the limited space in the cylinderhead. An alternative means is to provide a single set of injectors forinjection of both the ethanol and the gasoline. Two options arepossible, one in which there is a single nozzle and valve (and thegasoline and ethanol are co-injected), and one in which each fuel has aseparate nozzle and valve.

Using direct injection of both the gasoline and the ethanol has thedisadvantage of increased cost. In addition to a sophisticated injectoror injectors, a second high pressure fuel pump is also needed. Theethanol and the gasoline also need to have parallel common plenums.

When a single nozzle is used, the ethanol and the gasoline aredistributed in the same manner in the cylinder. In the case with asingle nozzle and single valve, the fuels need to be mixed prior to thevalve/nozzle part of the injector. This could be done either outside ofthe injector or in the injector body. The volume between the mixingpoint and the nozzle should be minimized to allow for fast response ofthe fuel mixture.

A slight modification of the above embodiment involves an injector thathas two valves but a single nozzle. This minimizes the need for a secondvalve outside the injector for controlling the gasoline/ethanol mixture,in addition to minimizing the volume between the mixing point and thevalves.

It is possible to use a separate nozzle/valve for each fuel in a singleinjector. In this case, the gasoline and the ethanol can be deposited indifferent regions of the cylinder. An additional advantage would be toprovide different spray patterns for the ethanol and for the gasoline.This would provide the most flexible system (comparable to twoindependent injectors), with possibilities of simultaneous orasynchronous injection of varying fractions of ethanol/gasoline, as wellas being able to deposit the ethanol and the gasoline in the desiredlocation of the charge, for optimal non-uniform distribution of ethanolin the cylinder. Optimal distribution means knock avoidance with minimalconsumption of ethanol, while maintaining engine drivability. Optimalnon-uniform ethanol distribution can be obtained by centrally depositingthe gasoline and by preferentially depositing the ethanol in theperiphery of the cylinder, where the end gas will be. This can beaccomplished more easily with direct injection as opposed to achievingnon-uniform distribution of the gasoline through non-uniform spraying inthe inlet manifold. Because the heat of vaporization of the gasoline issubstantially lower than for ethanol (a factor of 4 smaller on an energybasis), the cooling effect in the region near the spark is smaller,affecting less the initial flame propagation. In addition, it may bebeneficial to retard the injection of the ethanol with respect to thegasoline.

When the ethanol has been exhausted, the engine can operate in a lowerperformance gasoline only' mode with turbocharger boost decrease (e.g.by a wastegate) and elimination or avoidance of operation at maximumtorque levels. These conditions could be limiting, and in some cases ameans of operating the vehicle at higher loads would be desired. Thiscould be accomplished by using gasoline in the ethanol system withgasoline direct injection (GDI), while at the same time port-fuelinjecting a fraction of the gasoline. Under these conditions the enginewill operate at higher loads and higher torques, but still far belowwhat ethanol could achieve. Only the cooling effect of the directinjection fuel is obtained, since the directly injected fuel has thesame octane number as the port-injection fuel (gasoline in both cases).

If the ratio of ethanol in the ethanol fuel tank to gasoline in thegasoline fuel tank is lower than a predetermined value (because of thelack or availability of ethanol or for some other reason), it ispossible to change the engine operation condition such that theethanol/gasoline consumption ratio over a drive cycle is decreased. Thisis done for reducing the maximum ethanol fraction at a given enginespeed that can be used in the engine. The allowed level of turbochargingand the maximum pressure, torque and horsepower would be correspondinglyreduced to prevent knock. In this way, a continuous tradeoff between theethanol/gasoline consumption ratio and the maximum torque and horsepowercan be accomplished.

By proper expert system evaluation of the recent ethanol/gasoline usageand amounts of gasoline and ethanol it is possible to provide means tominimize the need of the ‘low performance, gasoline only’ mode. Theusage of the antiknock agent can be restricted when the amount left inthe tank is below a predetermined level, such that the main fuel will beexhausted prior to or simultaneously with the ethanol. It would bedesirable to place a switch so that the operator could override thelimitations, in those conditions where the desired vehicle operationwill not be limited by the exhaustion of the antiknock agent.

Over a drive cycle, the amount of ethanol (by energy) required toenhance the octane number sufficiently to increase efficiency by atleast 25% would be less than 15% of the fuel (ethanol+gasoline energy)without ethanol stratification and less than 5% with ethanolstratification.

Onboard separation of ethanol from diesel by fractional distillation hasbeen demonstrated for use in ethanol exhaust aftertreatment catalysts[“Fuel-Borne Reductants for NOx Aftertreatment: Preliminary EtOH SCRStudy”, John Thomas, Mike Kass, Sam Lewis, John Storey, Ron Graves,Bruce Bunting, Alexander Panov, Paul Park, presented at the 2003 DEER(Diesel Engine Emissions Reduction) Workshop, Newport R.I. August 2003].This approach could be employed for onboard separation of ethanol from agasoline mixture. However, use of membrane separation can be simpler andless expensive. Although there is information about the use of membranesfor the separation of ethanol from water, to our knowledge there is noavailable information on the membrane separation of ethanol fromgasoline. Because the ethanol molecule is on the order of 4 Angstromsand the typical hydrocarbon fuel molecules are much larger, it ispossible to use membranes for the separation. Both organic and inorganicmembranes could be used. Since it is not necessary to obtain high purityethanol, the process is relatively simple and requires low pressure.

Both porous and transfusion membranes can be used because ethanol withtwo carbon atoms has significantly different properties than most othergasoline compounds which have five to ten carbon atoms. The otherantiknock agents contemplated for use in this invention also have asmall number of carbons relative to gasoline. For example, methanol hasone carbon. The membrane approach can be significantly simpler than thedistillation or absorption/desorption approaches (see Ilyama et al, U.S.Pat. No. 6,332,448) that have been suggested for separation of variousgasoline/diesel fuels where there is much less of a difference in thenumber of carbon atoms.

The location of the membrane could be in the region of high pressure inthe fuel line (downstream from the pump), or upstream from it. If it islocated downstream, the separation occurs only when the engine isoperational and the pump is on, while if it is upstream the separationis continuous. The pressure of the fuel downstream from the pump is afew bars (characteristic of port fuel injection). This is to bedifferentiated from the pressure of the ethanol system, which isdirectly injected and thus requires much higher pressures.

The separated ethanol is transported to a separate tank where it isstored. If there is too much ethanol, three options are available: 1.)additional separation is stopped; 2) some ethanol is used in the engine,even if not required 3) ethanol is returned to the main gasoline tank.

The tank should be reachable, in order to be able to introduceadditional ethanol when required, as when towing, in high temperatures,or when doing extensive climbing, conditions that require operation athigh torque and which if for extended periods of time would consumeethanol at a rate higher than what can be extracted from the fuel.

Extraction of ethanol from the gasoline can have the unintended effectof reducing the octane of the rest of the fuel. Thus, it is likely thatsomewhat increased use of injected ethanol would be required to preventknock. Even in the case without non-uniform distribution of the ethanol,under normal driving conditions the system can be designed so that theamount of ethanol extracted from the fuel matches the required ethanol.

It may also be advantageous to separate the ethanol from agasoline/ethanol mixture at the fueling station. As with onboardseparation, this approach also allows use of the present fueltransportation infrastructure. The potential advantages could be greaterflexibility in choice of a fuel separation system and lower costrelative to onboard separation. It may be of particular interest duringthe introductory phase of ethanol boosted engine vehicles.

It can be useful to have the capability to adjust the volume of theethanol tank, thus varying the maximum amount of ethanol in the ethanoltank. This capability would make it possible to drive longer distancesbetween ethanol refueling and to operate on different gasoline/ethanolratios over a drive cycle, depending on the availability and cost ofethanol and gasoline. In some cases, it may be advantageous to use moreethanol than is needed to provide the desired octane enhancement (e.g.,to meet alternative fuel or CO₂ reduction goals). It is desirable tohave this capability without increasing the overall fuel tank size. Asingle fuel tank with a membrane or plate separating variable amounts ofgasoline and ethanol can be used to accomplish this goal.

The tank can be configured to have a horizontal or verticalmoveable/deformable walls that are substantially impervious and separatethe regions that are filled with gasoline and ethanol. Separate fillingports and fuel lines are incorporated for each region as shown in FIGS.4 a and b. The separation between the gasoline and ethanol (or otherantiknock agent) does not have to be perfect since a small amount ofleakage of one fuel into the other will not adversely affect operationof the vehicle. The wall can be moved in response to the amount ofeither fuel in the tank. This process is automatic in the case of aseparating membrane, and the latter can be more impervious to leaks fromone fuel to the other.

Ethanol is denser than gasoline. The movable/deformable wall can beplaced such that the ethanol is located either on top of the gasoline orbelow the gasoline. However, since it is expected that less ethanol isrequired than gasoline, the preferred embodiment has the ethanol abovethe gasoline, as shown in FIG. 5.

If the ethanol is stored so that it is separate from the gasoline, itcan be mixed with various additives to insure the desired operation ofthe ethanol injection system. In addition, it is possible to usegasoline-ethanol mixtures, such as E85 (which contains 15% by volume ofgasoline). The lubricity additives include fatty acids, organic aminesalts (amine salts of acid phosphates and polyethyleneoxy acidphosphates), alkyl and aryl acid phosphates and dialkyl alkylphosphonates.

The modeling calculations show that for direct injection of alcohols,the larger impact of knock suppression is not the intrinsicknock-resistance of the fuel antiknock agent but rather its high heat ofvaporization. In order to evaluate alternatives to ethanol, Table 3shows the properties of proposed fuel antiknock/alternative fuels.Although some of these additives have higher octane numbers thangasoline, some of them have a much larger effect on the cylinder chargetemperature (Table 3 assumes injection after the inlet valve hasclosed). Some of these additives (mostly the ethers) have a comparablecharge temperature effect to that of gasoline direct injection, and thusare of less interest. The alcohols have optimal properties for theapplication, with temperature changes that are a factor of 3 or largerthan the temperature change due to gasoline direct injection (for 100%or near 100% operation with the additive). For ethanol, the change intemperature is a factor of more than 4 larger than that of gasoline, andfor methanol the change is about 9 times larger. The temperaturedecrease of the air increases with the amount of oxygen in the fuel (interms of the O/C ratio). Thus, it is highest for methanol, with an O/Cratio of 1, second for ethanol (O/C=2), and so on.

TABLE 3 Antiknock properties of various fuels (calculated from dataobtained in SAE standard J 1297 Alternative Automotive Fuels, September2002) Latent Vaporization Equiv Latent Net heat of heat of energy/ Stoicheat of ΔT (R + Combustion vaporization heat of air/fuel vaporizationair Fuel Type Chemical formula RON MON M)/2 MJ/kg MJ/kg combustion ratioMJ/kg air K Gasoline 42.8 0.30 0.007 14.6 0.020 −28 Ethyl t-Buytl EtherCH3CH2—O—C(CH3)3 118 102 110 36.3 0.31 0.009 12.1 0.026 −35 t-AmylMethyl Ether C2H5 C (CH3)2—O—CH3 111 98 105 36.3 0.32 0.009 12.1 0.027−36 Toluene C7H8 111 95 103 40.5 0.36 0.009 13.5 0.027 −37 Methylt-Butil Ether CH3—O—C(CH3)3 116 103 110 35.2 0.32 0.009 11.7 0.028 −37Diisopropyl Ether (CH3)2CH—O—CH(CH3)2 110 97 103 38.2 0.34 0.009 12.10.028 −39 t-Butly Alchohol (CH3)3 C—OH 103 91 97 32.9 0.60 0.018 11.10.054 −74 Isopropanol (CH3)2CHOH 118 98 108 30.4 0.74 0.024 10.4 0.071−97 Methanol with 50% methanol/TBA 114 96 103 26.5 0.88 0.033 8.8 0.100−137 cosolvent Ethanol CH3CH2OH 129 102 115 26.7 0.91 0.034 9 0.102 −138Methanol CH3OH 133 105 119 20.0 1.16 0.058 6.4 0.181 −246

Also shown in Table 3 are the ratios of the heat of vaporization to theheat of combustion, a measure of the potential effects when used asantiknock agents. This parameter gives a measure of the amount ofevaporative cooling for a given level of torque. The last entry,ΔT_(air), measures the decrease in air temperature for a stoichiometricmixture with injection after the inlet valve closes. Although the effectclearly is maximized by the use of methanol, other considerations maymake ethanol the preferred choice. Methanol is toxic and corrosive.

Hydrous ethanol (with a small amount of water) has the advantage oflower cost than pure (neat) ethanol. Removing the last 10% to 15% waterfrom ethanol has significant expense and consumes considerable energy.Manufacturing facilities typically produce ethanol with about 10% waterby volume unless there is a need for essentially pure (anhydrous)ethanol. It could be advantageous to use ethanol with a waterconcentration of 5% to 15% by volume.

By using a closed loop approach to identify engine knock, flexiblegasoline grades (with different octane ratings) and flexibleknock-prevention fuel grades can be used. An open loop system wouldrequire measurement of the quality of the antiknock additive. Similarly,an open loop system would require determining the quality of the fuel(octane number). Closed loop operation allows the use of less expensivegasoline, when available, thus partially compensating for the moreexpensive anti-knock agent. It is also possible to use differentantiknock fuel according to its availability, such as ethanol in theregions that produce and process corn, and methanol in those that havemethanol production capabilities. Thus, the least expensive grade ofgasoline available and the least expensive antiknock fuel can be used,allowing a decrease of the cost of operating the vehicle as well asincreasing the availability of the antiknock fuel.

Although the above discussion has featured ethanol as an exemplaryanti-knock agent, the same approach can be applied to other high octanefuel and fuel additives with high vaporization energies such as methanol(with higher vaporization energy per unit fuel), and other anti-knockagents such as isopropanol, tertiary butyl alcohol, or ethers such asmethyl tertiary butyl ether (MTBE), ethyl tertiary butyl ether (ETBE),or tertiary amyl methyl ether (TAME). It may be advantageous to usevarious mixtures of these fuels and additives with each other and withethanol.

Particularly during the introduction phase of the present invention, theethanol fueling could be performed by the use of containers, such asone-gallon containers. To facilitate ease of fueling an expandable pipeand funnel can be built into the ethanol fuel tank of the vehicle.

The ethanol in these containers would be denatured so as to preventhuman consumption as an alcoholic beverage and could contain theadditives described above. Ethanol sold for fuel, such as in Brazil, isdenatured by a small fraction of gasoline (2%) among other denaturingagents (methanol, isopropanol and others).

Recycling of the container could take place at certain specificlocations such as gasoline stations.

Using a signal from a knock sensor to determine when and how muchethanol or other anti-knock agent must be used at various times in adrive cycle to prevent knock, the fuel management system can be employedto minimize the amount of ethanol or other anti-knock agent that isconsumed over the drive cycle. If sufficient ethanol or other anti-knockagent is available, the fuel management system can also be used toemploy more ethanol than would be needed to prevent knock. This wouldallow greater gasoline savings (the gasoline savings component fromsubstitution of ethanol for gasoline would increase) and carbon dioxidereduction. In this case it may he desirable to operate at an anti-knockagent fraction which is either varied or constant during the drivecycle.

The contents of all of the references cited in this specification areincorporated by reference herein in their entirety.

It is recognized that modifications and variations of the inventionsdisclosed herein will be apparent to those of ordinary skill in the artand all such modifications and variations are included within the scopeof the appended claims.

What is claimed is:
 1. A fuel management system for a turbocharged sparkignition engine that employs a first fueling system that directlyinjects fuel as a liquid into at least one engine cylinder and a secondfueling system that introduces fuel into a region outside of thecylinder where: during part of the drive cycle there is a range oftorque where both fueling systems are used at the same torque and thefraction of fuel in the engine cylinder that is provided by the firstfueling system is increased so as to meet the requirement for increasedknock resistance as the torque and speed of the engine are changed and;where a control system using information from a knock detector is usedto increase the fraction of fuel in the engine cylinder that is providedby the first fueling system.
 2. The fuel management system of claim 1where the increase in the fraction of fuel in the engine cylinder thatis provided by the first fueling system so as to prevent knock asincreased knock resistance is required is minimized by dosed loopcontrol.
 3. The fuel management system of claim 2 where a microprocessorand open loop control used in the control system.
 4. The fuel managementsystem of claims 1 and 2 where the highest fraction of fuel from thefirst fueling system is provided when the highest knock resistance isneeded.
 5. The fuel management system of claim 4 where the first fuelingsystem alone is used when the highest knock resistance is needed.
 6. Thefuel management system of claims 4 where the highest fraction of fuelfrom the first fueling system is utilized when the engine is operated atlow rpm.
 7. The fuel management system of claims 1 and 2 where whenspark retard is decreased the fraction of fuel provided by the firstfueling system is increased.
 8. The fuel management system of claims 1and 2 where the second fueling system uses port fuel injection.
 9. Thefuel management system of claims 1 and 2 where gasoline is introducedinto the engine.
 10. The fuel management system of claims 1 and 2 whereethanol is introduced into the engine.
 11. A fuel management system fora turbocharged spark ignition engine that employs a first fueling systemthat directly injects fuel as a liquid into at least one engine cylinderwhere the injection occurs after at least one inlet valve for admittingair to the cylinder has closed and a second fueling system thatintroduces fuel into a region outside of the cylinder and; where duringat least part of the drive cycle there is a range of torque where bothfueling systems are used at the same torque and the fraction of fuel inthe engine cylinders that is provided by the first fueling system isincreased so as to meet the requirement for increased knock resistanceas the torque and speed of the engine are changed.
 12. The fuelmanagement system of claim 11 where the maximum knock free torque isincreased relative to the maximum knock free torque if the directinjection occurred before the inlet valve was closed.
 13. The fuelmanagement system of claims 11 and 12 where when both fueling systemsare used combustion stability is greater than when the first fuelingsystem is used alone.
 14. The fuel management system of claim 11 wherespark retard is decreased when the fraction of fuel delivered to theengine cylinder from the first fueling system is increased.
 15. The fuelmanagement system of claim 11 where closed loop control using a knockdetector is employed.
 16. The fuel management system of claim 15 wherethe fuel management system minimizes the fraction of fuel delivered tothe engine cylinder from the first fueling system as the torque isincreased.
 17. The fuel management system of claim 16 where open loopcontrol and a microprocessor are employed.
 18. The fuel managementsystem of claim 11 where gasoline is introduced into the engine.
 19. Thefuel management system of claim 11 where ethanol is introduced into theengine.
 20. The fuel management system of claim 11 where the secondfueling system introduces fuel by port fuel injection.
 21. The fuelmanagement system of claim 11 where the second fueling system introducesfuel into the manifold.